The present invention relates to treatment of the blind regions in a person's visual field.
Damage to the visual system, as used herein, is defined as impairment of any structure (or of all structures) involved in the processing of vision. These structures include, but are not restricted to, the nervous system tissue from the level of the retina, including the retina up to the optic nerve and all brain structures involved in visual processing. Such damage leads to deficits or even a loss of visual functions which may result in partial or more or less complete blindness. This damage may come from many sources and may include damage to the retina or damage to the visual cortex, specifically the primary visual cortex (V1). Damage to the visual system can be due to causes that include trauma, stroke, tumor growth or inflammatory diseases. The retina may also be damaged by retinal detachment, laser damage or other causes, such as glaucoma or age related macular degeneration. Damage to the retina shall be referred to herein as “retinopathies.”
Perimetry methods (static or kinetic) systematically measure the visual field function of a subject and are used to identify regions of the visual field in which vision is normal, reduced, or absent (blind).
Treatment of a zone of deteriorated vision or residual visual function or partial visual system injury (“transition zone”) has been taught in U.S. Pat. No. 6,464,356 and the treatment of zones of intact vision has been taught in U.S. patent application Ser. No. 10/503,869 (publication number 2005/0213033) both of which are incorporated herein by reference in their entirety.
The “blind zone,” however, has not been considered amendable to remedial treatment. The reason for this was that once the visual cortex is damaged, the assumption was that no vision restoration is possible. However, in recent years several authors have described neuronal pathways in the brain which bypass the damaged cortex and are therefore often not affected by the injury. These are typically referred to as “extrastriate” pathways and permit information to travel from the retina to higher processing centers of the brain, thereby bypassing the primary visual cortex or other damaged regions.
In the normal brain these pathways are believed to be involved in the perception of moving visual stimuli and consequently, when the primary visual cortex is damaged, they still maintain the patients ability to see (or guess correctly) moving stimuli without the patient having a full awareness of the visual stimuli. This phenomenon is known as “blindsight”.
It is a well recognized problem that patients with damage to the primary visual pathway can not see visual stimuli, thus having areas of complete or partial blindness. While current stimulative treatment paradigms may help regain some of the lost vision, the approach of this prior art is to stimulate areas of residual vision (ARVs) of the damaged primary pathway itself, where some residual vision can be found at the time of commencement of therapy. However, the progress achieved by stimulating surviving cells in the primary system is very labor intensive and may not achieve complete restoration. Therefore, methods are desirable whereby faster or more complete restoration may be achieved.